figuring out where mail is coming from

[urgrue <urgrue@xxxxxxxxx>]

i would deduce from this log snippet that this particular mail was sent by 
my own server, would this be a correct deduction? are there alternative 
interpretations? because the mail in question was quite obviously loaded 
with a trojan or virus.

Mar 27 09:45:00 mail sendmail[19487]: i2R7j0919487: from=postmaster, 
size=6479, class=0, nrcpts=1, 
msgid=<200403270745.i2R7j0919487@xxxxxxxxxxxxxxxxx>, relay=root@localhost
Mar 27 09:45:00 mail sendmail[19490]: i2R7j0919487: to="|exec 
/usr/bin/procmail", ctladdr=freddie (500/100), delay=00:00:00, 
xdelay=00:00:00, mailer=prog, pri=126479, dsn=2.0.0, stat=Sent

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